This invention relates to an active-energy-ray curable coating composition and more particularly it relates to active-energy-ray curable compositions comprising an acrylic copolymer having (meth)acrylyloxy groups linked to functional groups of side chains and an unsaturated compound having two or more crosslinkable bonds.
In recent years, active-energy-ray curable coating compositions have been used in various fields by taking advantage of the excellent surface hardness and mar resistance of cured coating films formed therefrom. However, in some cases, they could not be used in dry film resists, transfer foils, etc., which require attachment of a film or additional coating immediately after coating.
The reason for this disadvantage is that conventional active-energy-ray curable coating compositions are composed mainly of monomers or liquid oligomers as highly volatile components. Even when a solvent good in drying characteristics or a solid oligomer is used, a coating film formed by coating the resulting composition is poor in dry tack and is sticky for a long period of time, resulting in retention of tack.
To improve these tacky films it is known to blend a thermoplastic resin which is good in dry tack, such as acrylic resin or nitrocellulose lacquer, with these conventional active-energy-ray curable coating compositions. However, since such thermoplastic resins cannot be cured by active energy rays, these blends provide a coating composition which is inferior to conventional active-energy-ray coating compositions in film performances such as surface hardness, mar resistance, and wear resistance after irradiation with active energy rays. Thus, prior to our discovery, no coating composition provided the performance characteristics discussed above when cured by irradiation with active energy rays after processing, such as attachment of a film or additional coating immediately after coating, as in the case of use in the above-mentioned dry film resists, transfer foils, etc.
Exemplary of these conventional problems is that which arises in providing active-energy-ray curable coating compositions for transfer foils. In transfer foils used for decorating plastic molded articles, thermoplastic resins such as halogenated rubber resins and thermoplastic acrylic resins have heretofore been used as a varnish release layer which forms the surface of a final product after decoration. However, this method is disadvantageous in that the transfer foils are insufficient in surface hardness and chemical resistance. Therefore, it has been proposed that a resin curable by active energy rays, such as ultraviolet rays, be used as a varnish release layer and cured after release to form the surface of final product.
For example, Japanese Patent Application Kokai (Laid-Open) No. 144994/81 discloses that a varnish release layer is formed by using a coating composition prepared by blending a reactive diluent with urethane acrylate obtained by reacting an urethane prepolymer having an isocyanate group at the end (obtained by reacting a polyol with a dissocyanate) with an acrylate having a hydroxyl group, or by blending a reactive diluent with an epoxyacrylate obtained by ester-addition of acrylic acid to an epoxy resin. Japanese Patent Application Kokai (Laid-Open) No. 148580/81 discloses that such a coating composition as described above is used in a bonding layer between a patterned layer and an object on which transfer printing is to be conducted.
Japanese Patent Application Kokai (Laid-Open) Nos. 49591/82, 171988/83 and 171989/83 disclose the formation of a varnish release layer using an ultraviolet ray curable coating composition or an electron ray curable coating composition.
However, when desired printing of a pattern or the like on such a conventional varnish release layer as explained above is attempted, no beautiful printed surface is formed because the varnish release layer is insufficient in drying characteristics and hence is sticky for a long period of time. Furthermore, even when printing can be achieved, release of a release film after transfer is difficult. We conjecture that this is so because conventional active-energy-ray curable coating compositions comprise liquid oligomers as their main constituent. Indicative of this is the observation that even when a solvent good in drying characteristics is used, the coated surface is still sticky and hence retains tack after evaporation of the solvent.
Accordingly, it would be desirable in the art to have an active-energy-ray curable coating composition which is so improved in dry tack that a pattern or the like can be beautifully printed in production of a transfer foil, and which not only cures well when irradiated after transfer to a molded article or the like and provides easy release of a release film, but also yields a coating film after irradiation which has good performance characteristics, such as pencil hardness, mar resistance, wear resistance, chemical resistance, ligh resistance, weather resistance, heat resistance, etc. The performance characteristics sought in any particular application will depend upon the use of the coating film.